Aryl amines are attractive targets for chemical synthesis because of their wide utility in fine chemicals, dyes and polymers. High purity triarylamines find application in xerographic photoreceptors where, as concentrated solid solutions in polymeric transport layers, they function as efficient hole conductors (U.S. Pat. Nos. 5,648,539 and 4,265,990). Triarylamines are also important to a number of emerging technologies like nonlinear optical chromophores useful in the design of integrated electrooptic switches and modulators (U.S. Pat. Nos. 5,654,482 & 5,723,671). Various methods have been described in the prior art for the preparation of arylamines. There are several reports in the prior art on the synthesis of aryl amines (U.S. Pat. Nos. 5,648,842 & 5,654,482). These and other prior art illustrate the Ullmann condensation reaction at high temperatures like 160° C. using non ligated cuprous oxide as catalyst. The drawback of these processes is that they are prone to produce troublesome impurities due to high operating temperatures, necessitating extensive purification. This becomes important for applications in charge transporting molecules in xerographic imaging and other electronic applications. European Patent Publication EP 0 617 005 A2 discloses the synthesis of certain aryl amines using copper catalyst in the form of metallic copper powder, copper sulfate, cuprous oxide, copper iodide or copper nitrate. However, the drawback of this process is also the use of very high temperatures such as 200° C. and very high reaction times such as 30 hours. Thus there is a need to develop improved catalyst system, which operates at lower reaction temperatures and preferably for shorter reaction times. There are several reports on the use of ligated copper catalyst, which operates at lower temperatures (˜115° C.) (U.S. Pat. Nos. 5,705,697, 5,648,539, 5,723,671, 5,654,482 & 5,648,542). All these reports use only N-containing organic compounds and more specifically 1,10-phenanthroline as a ligand. There are few reports on the use of P-containing catalysts, which have good catalyst activity (Org. Lett. 3, 4315-4317, 2001), but no diphos ligands. However, in these cases use of preformed catalyst complex Cu (PPh3)Br is necessary and no arylamine formation was observed when CuCl and free phosphine were used as catalyst system (Tet. Lett. 42, 4791-4793, 2001). However the drawback of this process is requirement of very high reaction time (24-32 h) using primary amines/secondary amines as reactants.
Because of the commercial interest in arylamines, increasing academic as well as industrial attention has been paid towards research in developing new methods for their preparation. In view of the advantages and features of the present invention, the process of this invention would be a significant advancement in the current state of the art related to the synthesis of aryl amines.